Lambda表达式与标准运算符查询

class Program
{
    static void Main(string[] args)
    {
        //Lambda表达式输出List集合每一项
        List<string> list = new List<string>() { "aaa", "bbb", "ccc", "ddd", "eee" };
        list.ForEach(d => Console.WriteLine(d));

        //Lambda表达式查找匹配元素
        List a1 = new List();
        a1.Add(new A1 { Id = 10, Name = "aaa" });
        a1.Add(new A1 { Id = 11, Name = "bbb" });
        a1.Add(new A1 { Id = 12, Name = "ccc" });
        a1.Add(new A1 { Id = 13, Name = "ddd" });
        List list1 = a1.FindAll(d => d.Id > 11);
        //Lambda排序
        a1.Sort((x, y) => y.Id - x.Id);

        //Lambda匹配指定元素到新集合
        var s1 = a1.Select(d => new A2() { Name = d.Name });
        foreach (var item in s1)
        {
            Console.WriteLine(item.Name);
        }

        //Lambda演变过程
        var gg = new Func<string, int>(delegate(string str) { return str.Length; });
        int s = gg("abcde");
        var ss = delegate(string str) { return str.Length; };
        var qq = (string str) => { return str.Length; };
        var ww = (string str) => str.Length;
        var ee = str => str.Length;
        var bb = new Func<int, int, int>(delegate(int x, int y) { return x + y; });
        int cc = bb(5,10);
        Console.ReadKey();
    }
}
public class A1
{
    public int Id { get; set; }
    public string Name { get; set; }
}
public class A2
{
    public string Name { get; set; }
}

标准查询运算符-Where-Select-Order-Join

List a1 = new List();
a1.Add(new A1 { Id = 10, Name = "aaa", Age = 101, Gender = true });
a1.Add(new A1 { Id = 13, Name = "bbb", Age = 21, Gender = true });
a1.Add(new A1 { Id = 12, Name = "ccc", Age = 21, Gender = false });
a1.Add(new A1 { Id = 13, Name = "ddd", Age = 200, Gender = true });
List a2 = new List();
a2.Add(new DogToy { DogId = 11, DogName = "小白" });
a2.Add(new DogToy { DogId = 10, DogName = "小欢" });
a2.Add(new DogToy { DogId = 12, DogName = "小美" });
a2.Add(new DogToy { DogId = 15, DogName = "小王" });
//Join 连接集合
//返回的结果是一个匿名类集合，程序员可以手动的控制返回集合里使用联合查询
//两个集合里的的哪些属性
var listJoined = a1.Join(a2, d => d.Id, t => t.DogId,
    (d, t) => new { DogId = d.Id, DogName = d.Name, ToyName = t.DogName }).ToList();
listJoined.ForEach(d=>Console.WriteLine(d.ToString()));

//a1.ForEach(d => { Console.WriteLine(d.ToString()); });
//Where查询
//var aa = a1.Where(d => d.Gender == false);
//链式编程
//var aa = a1.Where(d => d.Gender == false).Select(d => new A2() { Name = d.Name });
//升序排序
//var aa = a1.OrderBy(d => d.Age).ToList();
//升序后再按指定列排序
var aa = a1.OrderBy(d => d.Age).ThenBy(d => d.Id).ToList();
//降序排序
//var aa = a1.OrderByDescending(d => d.Age).ToList();
//aa.ForEach(d => Console.WriteLine(d.ToString()));

标准查询运算符-GroupBy分组

List a1 = new List();
a1.Add(new A1 { Id = 10, Name = "aaa", Age = 101, Gender = true });
a1.Add(new A1 { Id = 13, Name = "bbb", Age = 21, Gender = true });
a1.Add(new A1 { Id = 12, Name = "ccc", Age = 21, Gender = false });
a1.Add(new A1 { Id = 13, Name = "ddd", Age = 200, Gender = false });
List a2 = new List();
a2.Add(new DogToy { DogId = 11, DogName = "小白" });
a2.Add(new DogToy { DogId = 10, DogName = "小欢" });
a2.Add(new DogToy { DogId = 12, DogName = "小美" });
a2.Add(new DogToy { DogId = 15, DogName = "小王" });
//Join 连接集合
//返回的结果是一个匿名类集合，程序员可以手动的控制返回集合里使用联合查询
//两个集合里的的哪些属性
var listJoined = a1.Join(a2, d => d.Id, t => t.DogId,
    (d, t) => new { DogId = d.Id, DogName = d.Name, ToyName = t.DogName }).ToList();
//遍历输出
listJoined.ForEach(d=>Console.WriteLine(d.ToString()));

//GroupBy分组,将姓别分组
var listGroup = a1.GroupBy(d => d.Gender);
foreach (var group in listGroup)
{
    //输出小组的分组条件
    Console.WriteLine("小组:" + group.Key);
    //遍历小组里所有的元素
    foreach (var item in group)
    {
        Console.WriteLine(item.ToString());
    }
}
//a1.ForEach(d => { Console.WriteLine(d.ToString()); });
//Where查询
var aa = a1.Where(d => d.Gender == false);
//链式编程
var aa = a1.Where(d => d.Gender == false).Select(d => new A2() { Name = d.Name });
//升序排序
var aa = a1.OrderBy(d => d.Age).ToList();
//升序后再按指定列排序
var aa = a1.OrderBy(d => d.Age).ThenBy(d => d.Id).ToList();
//降序排序
var aa = a1.OrderByDescending(d => d.Age).ToList();
aa.ForEach(d => Console.WriteLine(d.ToString()));

 //分页

List a1 = new List();
a1.Add(new A1 { Id = 10, Name = "aaa", Age = 101, Gender = true });
a1.Add(new A1 { Id = 15, Name = "bbb", Age = 21, Gender = true });
a1.Add(new A1 { Id = 12, Name = "ccc", Age = 21, Gender = false });
a1.Add(new A1 { Id = 13, Name = "ddd", Age = 200, Gender = false });
var list = a1.OrderBy(d => d.Id).ToList();
//分页,Skip(0)跳过0行,Take(2)分两行
//var pageOne = list.Skip(0).Take(2);
var pageOne = list.Skip(0).Take(10).ToList();
Console.WriteLine("第一页");
pageOne.ForEach(i => Console.WriteLine(i.ToString()));
var pageTwo = list.Skip(10).Take(10).ToList();
Console.WriteLine("第二页");
pageTwo.ForEach(i => Console.WriteLine(i.ToString()));

var pageOne1 = GetPagedListByIndex(a1, 1);
Console.WriteLine("第一页");
pageOne1.ForEach(i => Console.WriteLine(i.ToString()));

var pageTwo2 = GetPagedListByIndex(a1, 2);
Console.WriteLine("第二页");
pageTwo2.ForEach(i => Console.WriteLine(i.ToString()));
Console.ReadKey();
}

//分页方法
static List GetPagedListByIndex(List groupList, int pageIndex)
{
　　int pageSize = 10;
　　return groupList.Skip((pageIndex - 1) * pageSize).Take(pageSize).ToList();
}

 

转载于:https://www.cnblogs.com/genesis/p/4908612.html